## Question

###### Is exergonic the same as endothermic or exothermic?

## Answers

Exergonic refer to changes in the Gibbs free energy. Exothermic and endothermic refer to changes in enthalpy.

## Explanation:

Exothermic and endothermic refer to changes in enthalpy

#ΔH# . Exergonic and endergonic refer to changes in the Gibbs free energy#ΔG# ."Exo" and "exer" mean "out of". "Endo" and "ender" mean "into".

#ΔH# decreases for an exothermic process and increases for an endothermic process.

#ΔG# decreases for an exergonic process and increases for an endergonic process.For a given reaction, the change in Gibbs free energy is

#ΔG = ΔH − TΔS# .

#ΔG# is a measure of the spontaneity of a reaction. If#ΔG# is negative, the process is spontaneous. If#ΔG# is positive the process is not spontaneous.We have four possibilities:

1.#ΔH# < 0 and#ΔS# > 0 always gives#ΔG# < 0.The process is both exothermic and exergonic. It is

alwaysspontaneous.

2.#ΔH# > 0 and#ΔS# < 0 always gives#ΔG# > 0.The process is both endothermic and endergonic. It is

neverspontaneous.

3.#ΔH# > 0 and#ΔS# > 0.This gives

#ΔG# > 0 at low temperatures. The process is both endothermic and endergonic.At high temperatures,

#ΔG# < 0. The process is still endothermic but it has become exergonic. The process is spontaneous only at high temperatures.An example is the endothermic decomposition of calcium carbonate.

CaCO₃(s) → CaO(s) + CO₂(g).

ΔS is positive because the reaction produces a gas from a solid. CaCO₃ is stable at room temperature but decomposes at high temperatures.

4.#ΔH# < 0 and# ΔS# < 0.This gives

#ΔG# < 0 at low temperatures. The process is both exothermic and exergonic.At high temperatures,

#ΔG# > 0. The process is still exothermic but it has become endergonic. It is no longer spontaneous.An example is the exothermic synthesis of ammonia.

N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

Increasing the temperature increases the yield of ammonia. But it drives the position of equilibrium to the left.